Fiber Optic Cables – How They Works?

Table of contents

1) how optical fibers works

2) Total Internal Reflection

3) Absorption And Scattering

4) Refractive Index

5) How optical fiber transmit information?

Fiber Optic Cables – How They Works

Fiber Optic Cables - How They Works

 Optical fiber cable is made up of thousands of fiber strands. And a single fiber strands as thin as a human hair.

 Optical fibers carry information in the form of light. Let’s first learn somefundame tak behaviors of light to understand the workings of optical fibers.

  And this change in speed is expressed by the refractive index. This variation and the speed of the light leads to another interesting phenomenon. Refraction, to understand what it is, let us carry out a interesting experiment.

Experiment With Optical Fiber

 In this experiment, lightpasses through a prism. You can see that at the interface the light gets bent instead of going straight. This phenomenon is known as refraction. 

 Refraction occurs when light passes from a medium with a one refractive index to one with another refractive index.

Fiber Optic Cables - How They Works

Refractive Indices

 The light bends towards the interface when it goes from a medium of high to one of low refractive indices. 

Refraction is the reason why a pencil looks bent in a glass of water.

 This simple refraction technique is effectively used in optical fibers.


 Now, let’s make this experiment a hypothetical one. Using some dopants we are able to increase the refractive index of the glass in real time.

 As we increase the refractive index, the light will bend more and more towards the surface.

 After a time you can see that, the light will pass throughthe surface of the glass. If we increase therefractive index further, the light will suddenly comeback to the first medium as a pure reflection. This is called total internal reflection.

Total Internal Reflection

 The total internal reflection is possible if we increase the incident angle rather than increasingthe refractive index.

 In this case at a certain angle called the critical angle, the light will come backto the first medium.

Phenomenon of Total internal Reflection

 This phenomenon of total internal reflection is used in optical fibercables to transmit the light.

 The simplest form of opticalfiber cable is shown here. Cylindrical glass witha high refractive index. If the laser strikes the interface at an angle greater than the critical angle.

 Total internal reflection will happen and the light will reach the other end. This means that light can be confined in the optical fiber over a long distance. No matter what complexshape the fiber forms. 

 Remember, total internal reflection happens between the high refractive index glass and the low refractive index air. However, optical fibers need a protective coating.

Fiber Optic Cables - How They Works

Protective Material

 A protective coating is not possible with this configuration. The introduction of protective material will replace the position of the air and cease the total internal reflection phenomenon.

 An easy way to overcome this issue is to introduce a lowrefractive index glass above the core glass known as cladding.

Protective Lahar on Fibers

 This way total internal reflection will happen and we’ll be able touse a protective layer. Both the core and the cladding use silica as their base material.

 The difference in the refractive index can be achieved by adding different types of dopants. The optical fiber we have just constructed won’t be able to carry signalsfor more than 100 kilometers.

 This is due to various lossesthat happen in the cable. This loss of signal strength is generally called attenuation. 

Absorption And Scattering

Absorption and scattering are the main reasons for signal attenuation. This is why you see amplifiers and cables after a certain distance.

Signal Strength

 They boost the signal strength and allow signals to be transmitted over a long distance. The power required for the amplifier is drawn from nearby sources. Now, back to the main topic,

 how does the opticalfiber transmit information such as phone calls or internet signals?

 Any information can be represented in the form of zeros and ones. Assume you want to senda hello text message through your mobile.

Binary Codes

 First this word will be converted into an equivalent binary code as a sequence of zeros and ones. After the conversion yourmobile phone will transmit these zeros and ones in theform of electromagnetic waves.

 One is transmitted as a high frequency and zero as low frequency wave. Your local cell tower picks upthese electromagnetic waves. At the tower, if the electromagnetic wave is of high frequency, alight pulse is generated. 

 No pulse is generated. Now these light pulsescan easily be transmitted through optical fiber cables.

 The light pulses which carry the information have to travel through ac complecated of cables to reach their destination.

optical fiber cables

 For this purpose, theentire globe is covered with optical fiber cables. A detailed cross sectionview of an undersea cable is shown here. You can see that only asmall portion of the cable is used for holding the optical fiber.

 The remaining area of the cable is a mechanical structure for protection and strength. 

 Wheredoes the amplifier get power from under these deep oceans?

 Well, for this a thin coppershell is used inside the cable. Which carries electricpower along the cable so that the amplifiers can be powered.

Mobile Communication

 This whole discussion simply means that if optical fiber cables do not reach a part of the globe, that part will be isolated from the internet or mobile communications.

 If we compare optical fiber cable to traditional copper cable,the optical fiber cable is superior in almost every way.

 Fiber optic cablesprovide larger bandwidth and transmit data at much higherspeeds than copper cables. This is because the speed of light is always greater thanthe speed of electrons.

Flow of Electrons

 The flow of electrons in a copper cable generates a magnetic fieldeven outside of the cable that can causeelectromagnetic interference. On the other hand, the light which travels through the opticalcable is always confined within the fiber.

 Thus the chance of interaction with an external signal does not exist. One more interesting feature about optical fiber cables is that any light signalwhich enters from the side has a minimal chance oftraveling along the cable.

 Thus the optical fiber cables provide high data security. You might be amazed toknow that optical fiber was first used in endoscopy even before it was used inthe telecommunications field.


 In telecommunications,digital pulses are transferred through the optical fiber cable. However, in endoscopic cables, visual signals whichare on the analog form are transmitted to the other end.

Career in Fiber Optics

Fiber Optic Cables - How They Works

here there networking pros. A quick and simple post on Fiber Optics so that you can sound like you sort of know what you’re talking about.

 I am not going to try to turn you into anexpert. In fact, even I am not an expert. And, for those of you who are familiar with my posts, you know I typically to make try to boil down the core essentials without goinginto a lot of theory.

So that you can get what you need to know in a very short amount of time. With that said, let’s get started.

 Fiber Optics….. there are a few things Ineed you to know so that if you ever have to work somebody who’s trying to get you todo something, or help you.

 First of all, these are fiber optic patchcables. And, I think we all know that way fiber opticsworks is by sending light through the cable which have a tiny glass or fiberglass conduitinside.

Advantage of Fiber optical fiber

 The big advantage of Fiber is that it cancarry LARGE amounts of data over long distances.

 So, first thing to mention since we’re talkingabout distances is the two cable mode types – Multi-mode and Single-mode. So, type types there. Now, just briefly, multi-mode is typicallyused for intra-building type connections.

 Like from one switch to another. Or, from one data room to another.

Optical fiber in Telephone Poles

 The single mode is typically for long distanceslike from 2-20 miles. That’s the stuff you see out on the telephone poles   

 The way you can tell the difference isthat even though the cables won’t have the mode type written on them.

 what you can dois, and I know the printing is small here so you may not be able to see it on the camera,but if you look closely, somewhere you will see a “micron size“.

 If you can see that right here, it says 62.5/125. So, the 62.5 is the inner-diameter, in microns,of fiber optic cable – it’s very tiny. 62.5 or 50 typcially means it’s a multi-modecable.

 Anything down around like 10 or 9 or 8 microns usually means single mode. Ok? the reason that is important is you can’tmix the mode-types.

 You can use a single mode cable where a multi-modeis called for. ok, 

the 2nd thing you need to know about isthe connector types. So, right now I’m holding in my hand what’s known as an “SC” connector.

 And, the way I’ve always memorized that isthat SC sort of sound like the begining of the word “Square“. I know that Square starts with “sq…”butthat little trick is what worked for me.

 Then, there is “ST” as in Sierra Tango. And, that is these kinda round, barrel connectors. Where they have the real long tips stickingout of the end. And, the last one, and this is the most commonone I see….. And, by the way, there are more than justwhat I have here. But, the last one I want to show you hereis “LC”. 

Which stands for Lucent Connector, but it’seasier for me to remember it as Little Connector. So, to recap – LC. ST. SC. OK, so….. can you mix connector types? Yes, you can.  

These cable just happen to be symmetrical. But, there such things as patch cable whereyou can mix the types.

 Not types of cable, but types of connectors. See?

 Here’s one where I’ve got SC on one end andST on the other. Alright? so…. we talked about Cable types- multi-mode and single mode. We talked about the connectors…. And, there’s another connector I don’t havewhich is known as MTRJ.

 Which is a very little, tiny guy. And, I really don’t see much of it. In fact, I’ll tell you, from my experience,used to see the ST and the SC a lot back in the last decade (2000-2010) or on older equipment.

 Typically, what I see about 90% of the timeis the LC connectors. OK? So, we talked about cable types and cabletype connectors. Now, what do these things do or what do they plug into?

 They plug into what is known as transceivers. Transceivers are the things that generateand receive the light. Now, they can either be standalone deviceslike this. Or, they can be built-in to switches or routers.

 You may notice these next time you’re lookingat a Cisco switch or Cisco router. You’ll see the little transceivers stickingout. And basically, what happens is here I’ve Transceiverwhich converts to ethernet.

 It’s got SC connectors on it. so, the sc connector fit in here. they are usually keyed, but not always. Sometimes they are loose. But, I’m going to show you something reallyimportant here in just a minute.

 So, see how that fits in there? Alright…. do you notice here on this transceiverI’ve got a TX and an RX? Now, you’re not always going to be lucky enoughto have those labels on some of the equipment you’re going to work with.

 But, here’s the key thing I want you to know. When you’re connecting two transceivers together,which is typically the case, you’re always going to want to have a cross-over.

 Meaning, that whatever is coming out of theTX (or Transmit) needs to go into the RX(or Receive) on the other side.

 Does that make sense?

 So, when light is being transmitted out ofthis port (TX), it needs to go in to the RX on the other port. So, if you’re ever working with fiber andyou can’t get a connection to work, there’s two things you can do:

 One, is you can checkto make sure the cable is flipping between your two transceivers. The second thing you can do is if you just,if it’s not working, you might as well just go ahead and take the chance, is just go aheadand pull it out and flip it over to see if that makes a difference.

 Ok… And, another newbie mistake a lot of us do. And, I have to admit that even I still dothis sometimes is, but you really should not, is DON’T look into the ends of the fiber tosee if you can see light. Reason why?

 It’s laser. It’s not good for your eyes. Also, don’t stare into transceivers that arepowered on. Don’t stare into the end of fiber cables whenthey’re live.

 Because, that laser light is not doing youreyes any favors. OK… so in the next video I do, we will talkabout. We will talk about the ways that you can useFiber to expand your network.

 And, about roughly how much it costs. And, where you can get the components. As well as what it takes. And, what it can do for expanding your localarea network. Alright… hope that helps you out. Thanks so much for reading.

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